Depression is the single biggest predictor of death for heart patients

In the paper, The association of depression at any time to the risk of death following coronary artery disease diagnosis, the team from the Intermountain Medical Center, was published in the European Heart Journal -- Quality of Care & Clinical Outcomes on July 28.

The study's lead author, Dr Heidi May, PhD, said: 'No matter how long or how short it was, patients were found to have twice the risk of dying compared to those who didn't have a follow-up diagnosis of depression.

'Depression was the strongest risk factor for dying, compared to any other risk factors we evaluated. That included age, heart failure, diabetes, high blood pressure, kidney failure, or having a heart attack or stroke.'

Dr May and her team from the Intermountain Medical Center Heart Institute studied 24,138 atients who had undergone angiographies to determine they had coronary artery disease.

To determine which of these patients subsequently developed depression, the team looked at standard diagnostic does called International Classification of Diseases codes.

The patients they found with depression were also placed into subcategories based on the length of time it took for their depression to be identified after their heart disease diagnosis.

This study is different to previous ones as it followed patients for an average of ten years after their coronary artery disease diagnoses to see if they ever became diagnosed with depression.

15 per cent, or 2,646 patients, were diagnosed with depression at some point in the followup period. Of this group, 27 per cent were diagnosed within one year of their heart event, 24 per cent between one and three years, nearly 15 per cent between three and five years, and nearly 37 per cent at least five years afterwards.

Dr May said: 'We've completed several depression-related studies and been looking at this connection for many years. The data just keeps building on itself, showing that if you have heart disease and depression and it's not appropriately treated in a timely fashion, it's not a good thing for your long-term well-being.'

The relationship is reciprocal: depression can result in worse outcomes for those with heart disease, and having heart disease can increase the likelihood of someone developing depression.

While the study could not point to a specific reason for this higher risk of death, Dr May thinks it could be to do with how patients with depression follow their treatment plans less closely.

She said: 'We know people with depression tend to be less compliant with medication on average and probably in general aren't following healthier diets or exercise regimens.

'They tend to do a poorer job of doing things that are prescribed than people without depression. That certainly doesn't mean you're depressed so you're going to be less compliant, but in general, they tend to follow those behaviors.

'Patients who have depression need to be treated for it to improve not only their long-term risks but their quality of life.

'I hope the takeaway is this: it doesn't matter how long it's been since the patient was diagnosed with coronary artery disease.

'After one year, it doesn't mean they're out of the woods. It should be ongoing, just like we keep measuring things like LDL cholesterol.'